Four switches are outside a room. Only one controls a light bulb inside. You can flip switches as much as you want but can only enter the room once. How do you determine which switch controls the bulb?
Hints
You need more information than just on/off.
Answer
This is a trick question—with only one bulb you cannot determine the correct switch among four with certainty using just on/off and heat. You can only identify one of three switches (like the classic 3-switch version). With four switches and one bulb, it's impossible.